15 Copyright © 2005, Oracle. All rights reserved. Container-Managed Relationships (CMRs)

15Copyright © 2005, Oracle. All rights reserved.

Container-Managed Relationships (CMRs)

15-2 Copyright © 2005, Oracle. All rights reserved.

Objectives

After completing this lesson, you should be able to do the following:

• Define relationships between entity beans

• Determine the cardinality and direction of a relationship

• Identify various elements of the deployment descriptor that define the relationship

• Develop CMR entity beans


Relationships


Implementing Relationships

• Data manipulation in the beans may involve a more complex data model, with a relationship between entity beans.

• The important aspects of a relationship are:– Cardinality: Number of data instances that can

participate in a relationship

– Direction: Direction in which a relationship is navigated


Cardinality and Direction of Relationships

• Cardinality:– One-to-one– One-to-many or many-to-one– Many-to-many

• Directionality:– Unidirectional– Bidirectional


One-to-One Relationships

• The phone_num column is the foreign key in the EMP entity that is referencing the PHONE entity.

• Each employee has only one phone number and each phone number belongs to only one employee.

111 1111Smith100

phone_numnameemp_id

MCI650111 1111

servicearea_codephone_num

EMP

PHONE


One-to-Many Relationships

Each department exists in only one location identified by location_id, whereas each location can contain many departments (1:M).

…Seattle1700

…citylocation_id

DEPARTMENTS

LOCATIONS

1700Administration10

location_iddepartment_namedepartment_id

1700Purchasing30


Many-to-Many Relationships

Each employee may be assigned many jobs and each job may be assigned to many employees.

SA_REP176A1

job_idemployee_idassign_pkASSIGNMENTS

EMPLOYEES

Jonathon176

Nameemployee_id

JOBS_HISTORY

...SA_REP

...job_id


Oracle TopLink

Oracle TopLink run-time framework:

• Facilitates data integration with enterprise applications

• Facilitates rapid development, deployment, and execution of all persistence-related aspects of any Java application

SQL

RowsJava

application

JDBCTopLink


TopLink: Integration of J2EE Applications with Data Sources at Run Time

DB2

SQL server

EIS

Oracle

XML

Data mapping and integration

EJBs

Servlets/JSPs

J2EEApplication Server


TopLink: Integrated with Oracle JDeveloper 10g


Implementing Relationships

• Relationship restrictions:– Define only for CMP 2.0 entity beans– Declare related CMP beans in one deployment

descriptor– Use only local interfaces to define the relationship

• Define abstract get() and set() accessor methods in the bean class for each relationship field

• In the deployment descriptor, define:– Name of each relationship– Cardinality and direction for each relationship– One section for each side of a bidirectional

relationship– Cascade delete operations on one side of the

relationship


Defining Abstract Accessor Methods

• Name: – get<cmrfieldname> and set<cmrfieldname> – Example: getDepartment(),

setEmployees(EmpLocal emp)

• Return type: – Local interface of the target bean for single object

retrieval– Collection or set of local interface objects for

multiple object retrieval

• Location where it is defined:– Only in the source bean for unidirectional

relationship– In both beans for bidirectional relationship


Accessor Methods in 1:1 Relationships

For bidirectional relationships, define abstract get() and set() accessor methods for CMR fields in both the abstract bean classes.

public abstract class Emp implements EntityBean {...public abstract PhoneLocal getPhone_PhoneNo();public abstract void setPhone_PhoneNo(PhoneLocal p);...

public abstract class Phone implements EntityBean {...public abstract EmpLocal getEmp_EmployeeID();public abstract void setEmp_EmployeeID(EmpLocal e);...


Accessor Methods in 1:M Relationships

public abstract class DepartmentsBean implementsEntityBean{...public abstract LocationsLocal getLocations_locationId();public abstract void setLocations_locationId (LocationsLocal locations_locationId);...

public abstract class LocationsBean implements EntityBean {...public abstract Collection getDepartments_locationId();public abstract void setDepartments_locationId(Collection departments_locationId);...


Checking Relationship Mappings in JDeveloper


Accessor Methods in M:N Relationships

public abstract class EmployeesBean implementsEntityBean{ ...public abstract Collection getJobHistory_employeeId();public abstract void setJobHistory_employeeId(Collection jobHistory_employeeId);... }

public abstract class JobHistoryBean implements EntityBean { ...public abstract Collection getEmployees_employeeId();public abstract void setEmployees_employeeId(Collection employees_employeeId);... }


Implementing a Relationship inthe Deployment Descriptor


Implementing 1:1 Relationships

... <relationships> <ejb-relation> <ejb-relation-name>EMP-PHONE</ejb-relation-name>

<ejb-relationship-role> <ejb-relationship-role-name>

Emp-has-Phone </ejb-relationship-role-name> <multiplicity>One</multiplicity> <relationship-role-source>

<ejb-name>Emp</ejb-name> </ relationship-role-source>

<cmr-field><cmr-field-name>Phone</cmr-field-name><cmr-field-type>PhoneLocal</cmr-field-type>

</cmr-field> </ejb-relationship-role>

...

Emp to Phone


Implementing 1:1 Relationships

... <ejb-relationship-role>

<ejb-relationship-role-name>Phone-has-Emp

</ejb-relationship-role-name> <multiplicity>One</multiplicity>

<cascade-delete /> <relationship-role-source>

<ejb-name>Phone</ejb-name> </ relationship-role-source>

<cmr-field><cmr-field-name>Emp</cmr-field-name><cmr-field-type>EmpLocal</cmr-field-type>

</cmr-field> </ejb-relationship-role></ejb-relation>

</relationships> ...

Phone to Emp


Implementing 1:M Relationships

<relationships> <ejb-relation> <ejb-relation-name>Departments-Locations

</ejb-relation-name> <ejb-relationship-role>

<ejb-relationship-role-name>Locations-has- departments_locationId </ejb-relationship-role-name>

<multiplicity>One</multiplicity> <relationship-role-source> <ejb-name>Locations</ejb-name> </relationship-role-source> <cmr-field> <cmr-field-name>departments_locationId

</cmr-field-name> <cmr-field-type>java.util.Collection

</cmr-field-type> </cmr-field> </ejb-relationship-role>...

Departments to Locations


Implementing 1:M Relationships

... <ejb-relationship-role> <ejb-relationship-role-name>Departments-owned-by-

locations_locationId </ejb-relationship-role-name> <multiplicity>Many</multiplicity> <relationship-role-source> <ejb-name>Departments</ejb-name> </relationship-role-source> <cmr-field> <cmr-field-name>locations_locationId

</cmr-field-name> </cmr-field> </ejb-relationship-role>...

Locations to Departments


Implementing M:N Relationships

... <ejb-relation> <ejb-relation-name>JobHistory – Employees

</ejb-relation-name> <ejb-relationship-role> <ejb-relationship-role-name>

JobHistory-has-employees_employeeId </ejb-relationship-role-name>

<multiplicity>Many</multiplicity> <relationship-role-source> <ejb-name>JobHistory</ejb-name> </relationship-role-source> <cmr-field> <cmr-field-name>employees_employeeId


</cmr-field-type> </cmr-field> </ejb-relationship-role> ...


Implementing M:N Relationships

<ejb-relationship-role> <ejb-relationship-role-name>

Employees-has-jobHistory_employeeId </ejb-relationship-role-name>

<multiplicity>Many</multiplicity> <relationship-role-source> <ejb-name>Employees</ejb-name> </relationship-role-source> <cmr-field> <cmr-field-name>jobHistory_employeeId


</cmr-field-type> </cmr-field> </ejb-relationship-role>


Mapping Relationship Fields to Database

• Accept default mapping provided by container (specify relationship fields in ejb-jar.xml)

• Explicitly map the fields to existing table columns in orion-ejb-jar.xml


Default Mapping of Relationship Fields

• Database: Specified in data-sources.xml• Each table in relationship: Same as for CMP entity

• Columns in each table: Based on <cmr-field>, which represents a bean in the relationship

• For each <cmr-field> of an entity, the container creates a foreign key to the primary key of the related entity:– In the source bean table for one-to-one mapping– In a container-generated association table for one-

to-many and many-to-many relationships

• User-defined or automatically generated primary key


Explicit Mapping of Relationship Fields

1. Deploy your application with only the ejb-jar.xml elements configured.

2. Copy the container-created orion-ejb-jar.xml file to your development environment.

3. Modify the <entity-deployment> element in the orion-ejb-jar.xml file to use the database table and columns that you specify.

4. Rearchive and redeploy your application.


Using JDeveloper to Create CMR Beans

Using JDeveloper, you can create a container-managed relationship between entity beans in the following ways:

• Create CMP beans from tables and generate default relationships between entities.

• Use the EJB Module Editor to specify the relationship or use TopLink Mapping Editor.

• Create an EJB Diagram for CMP beans and generate default relationships.


Summary

In this lesson, you should have learned how to:

• Determine the cardinality and direction of a relationship

• Define and implement relationships between CMR entity beans


Practice 15: Overview

This practice covers creating a one-to-many relationship between the Employees and Departments entity beans.

Documents

15 Copyright © 2005, Oracle. All rights reserved. Container-Managed Relationships (CMRs)